Electrochemical reactions in the field of eco-friendly energy

Exploitation of renewable and carbon-free energy conversion and storage techniques is critical for sustainable and eco-friendly development of human society. This thesis covers three important topics in this field including oxygen reduction reaction (ORR), electrochemical nitrogen fixation (NRR) and lithium-ion battery (LIB). Chapter-2: Carbon-based catalysts are promising candidates for replacing the expensive Pt-based catalysts in fuel cells. However, the structural-functional-relationship is hard to found due to the coexistence of multiple kinds of potentially ORR active sites. In this work, we employed holey-graphene materials as model catalysts to study the catalytical behavior of zigzag-edges on the ORR in both acidic and basic conditions. Chapter-3: Direct fabrication of single-atom catalysts (SACs) by microwave was developed. The as-prepared Cu-SAC exhibits excellent ORR activity and selectivity in both acidic and alkaline media. Incorporating Cu-SAC in holey-graphene strengthens the binding with oxygen, which enhances ORR activity, compared to incorporation in defective carbon. Considering the high conductivity and excellent stability against oxidation of the holey graphene, this work, for the first time, suggests that the contradictory structural requirement of carbon matrix for high catalytic activity and long-term durability can be unified and simultaneously satisfied. Chapter-4&5: NRR represents a potentially clean and sustainable alternative for the Haber-Bosch process. Current catalysts suffer low ammonia yield rate and selectivity due to poor nitrogen activation and competition with hydrogen evolution (HER). We developed a simple method for fast production of phosphorus-cation-doped WO3 (PWO3). The electronic modulation by phosphorus doping was systematically studied. PWO3 possesses high NRR performance. This work for the first time combines bulk intercalation of protons and phosphorus doping to simultaneously improve nitrogen activation and suppress HER, providing a new strategy for NRR catalyst design. Chapter-6: Aiming at better understanding of the initial stage of solid electrolyte interface formation process in LIB, we performed in-situ electrochemistry-combined atomic force microscopy during constant current (CC) and linear sweep (LS) lithiation. Based on the monitored morphology evolution of the electrode, models were built for understanding the Li+-solvent-cointercalation and solvent reduction processes. Parallel or competing relationships between these two processes were found responsible for the different morphologies after CC and LS lithiation.Ph.D.Includes bibliographical reference